<!-- 顶部导航 -->
<ul class="nav nav-tabs">
  <li class="nav-item"><a class="nav-link" [routerLink]="['/home']" routerLinkActive="active">首页</a></li>
  <li class="nav-item"><a class="nav-link" [routerLink]="['/user']" routerLinkActive="active">用户中心</a></li>
  <li class="nav-item"><a class="nav-link" [routerLink]="['/not-found']" routerLinkActive="active">关于</a></li>
  <li class="nav-item">
    <div ngbDropdown #myDrop="ngbDropdown"> 
      <a ngbDropdownToggle  class="nav-link" routerLinkActive="active"
       role="button" aria-haspopup="true" aria-expanded="false"> 更多</a>
      <div class="dropdown-menu dropdown-menu-left" aria-labelledby="dropdownMenu">
        <a class="dropdown-item" role="button" [routerLink]="['/home']">link - 1</a>
        <a class="dropdown-item" role="button" [routerLink]="['/user']">link - 2</a>
        <a class="dropdown-item" role="button" [routerLink]="['/not-found']">link - 3</a>
      </div>
    </div>
  </li>
</ul>